1. Field of the Invention
The invention relates to an improved method of controlling catalyst inventory in the reactor of an ebullated bed process. The method is used in conjunction with adding catalyst and relates to the determination of a catalyst inventory characterization factor.
2. Description of Other Relevant Methods in the Field
The ebullated bed process comprises the passing of concurrently flowing streams of liquids, or slurries of liquids and solids, and gas through a vertically cylindrical vessel containing catalyst. The catalyst is placed in random motion in the liquid and has a gross volume dispersed through the liquid medium greater than the volume of the mass when stationary. This technology has found commercial application in the upgrading of heavy liquid hydrocarbons or converting coal to synthetic oils.
The process is generally described in U.S. Pat. Re No. 25,770 to Johanson incorporated herein by reference. A mixture of hydrocarbon liquid and hydrogen is passed upwardly through a bed of catalyst particles at a rate such that the particles are forced into random motion as the liquid and gas pass upwardly through the bed. The catalyst bed motion is controlled by a recycle liquid flow so that at steady state, the bulk of the catalyst does not rise above a definable level in the reactor. Vapors along with the liquid which is being hydrogenated pass through that upper level of catalyst particles into a substantially catalyst free zone and are removed at the upper portion of the reactor.
In an ebullated bed process the substantial amounts of hydrogen gas and light hydrocarbon vapors present rise through the reaction zone into the catalyst free zone. Liquid is both recycled to the bottom of the reactor and removed from the reactor as product from this catalyst free zone. Vapor is separated from the liquid recycle stream before being passed through the recycle conduit to the recycle pump suction. The recycle pump (ebullation pump) maintains the expansion (ebullation) and random motion of catalyst particles at a constant and stable level. Gases or vapors present in the recycled liquid materially decrease the capacity of the recycle pump as well as alter the flow pattern within the reactor and thus decrease stability of the ebullated bed.
Reactors employed in a catalytic hydrogenation process with an ebullated bed of catalyst particles are designed with a central vertical recycle conduit which serves as the downcomer for recycling liquid from the catalyst free zone above the ebullated catalyst bed to the suction of a recycle pump to recirculate the liquid through the catalytic reaction zone. The recycling of liquid from the upper portion of the reactor serves to ebullate the catalyst bed, maintain temperature uniformity through the reactor and stabilize the catalyst bed.
U.S. Pat. No. 4,684,456 to R. P. Van Driesen et al. teaches the control of catalyst bed expansion in an expanded bed reactor. In the process, the expansion of the bed is controlled by changing the reactor recycle pump speed. The bed is provided with high and low level bed detectors and an additional detector for determining abnormally high bed (interface) level. The interface level is detected by means of a density detector comprising a radiation source at an interior point within the reactor and a detection source in the reactor wall. Raising and lowering the bed level changes the density between the radiation source and the radiation detector. It is apparent from the patent that the vertical range of steady state bed (interface) level as well as the highest and lowest steady state interface level is a design parameter.
U.S. Pat. No. 4,673,552 to A. S. Li et al. teaches a downwardly directed fluid flow distributor for recycle liquid in an ebullated bed reactor. The figures show the plenum 12 below the distributor grid 18 of reactor 14 contains inlet conduit 10, central conduit 24 and sparger ring 40. Ebullated catalyst bed 20 is supported on distribution grid 18 by a combination of recycle liquid and liquid and gas feed through tubes 26 and caps 28.
U.S. Pat. Nos. 3,410,791 to L. A. Perry et al.; 3,523,888 to N. C. Stewart et al. and 3,557,019 to R. P. Van Driesen teach an ebullated bed process wherein there is means for withdrawing catalyst from the bed and adding catalyst to the bed.
U.S. Pat. Nos. 3,412,010 to S. B. Alpert et al. and 3,363,992 to M. C. Chervenak teach an ebullated bed process. In the drawing is shown a catalyst bed interface and a catalyst level control. Also taught is an optional third, vapor phase filling the top of the reactor.
U.S. Pat. No. 3,398,085 to T. M. Engle teaches a process for catalyst addition and withdrawal in an ebullated bed process to maintain an average inventory of particulate solids in the reaction zone. Catalyst is introduced to a solids holding zone. The zone is purged of gases with oil and then sealed from the atmosphere. The sealed, oil filled catalyst zone is then pressured to reactor pressure and then transferred by liquid transport to the reaction zone by liquid phase transport. Solids are removed from the upper part of the reaction zone through a flow line at a rate corresponding to the rate transfer into the reaction zone by applying external gas under pressure to the flow line.